1. Field of the Invention
The present invention generally relates to a sleeve unit used for a fluid dynamic bearing assembly, a method of manufacturing the sleeve unit, and a motor using the fluid dynamic bearing assembly to which the sleeve unit is installed.
2. Description of the Related Art
Conventionally, a recording disk drive unit such as a hard disk device includes a spindle motor (hereinafter, simply referred to as “motor”) for rotary driving a recording disk. In such a bearing assembly utilizing fluid dynamic pressure, a thrust bearing portion or a radial bearing portion are formed with a shaft, a sleeve to allow the shaft to be inserted thereinto, and the like.
The Japanese laid open patent publication No. 2003-262217 discloses a spindle motor having a bearing unit with a sleeve inserted in a sleeve housing and a shaft to a tip end of which a thrust plate is attached. In the spindle motor, thrust bearing portions are defined in a gap defined between an upper end surface of the sleeve housing and a lower surface of the rotor hub, and in a gap between a lower end surface of the sleeve and an upper surface of the thrust plate.
The Japanese laid open patent publication No. 2006-77872 discloses a bearing unit having a similar configuration disclosed in the Japanese laid open patent publication No. 2003-262217. In the bearing unit disclosed in the Japanese laid open patent publication No. 2006-77872, a sleeve having dynamic pressure generating grooves arranged in axially upper and lower end surfaces thereof, and thrust bearing portions are defined in a gap between the upper end surface of the sleeve and a lower surface of the rotor hub, and in a gap between the lower end surface of the sleeve and the upper surface of the thrust plate.
In the bearing unit disclosed in the Japanese laid open patent publication No. 2006-77872, the upper end surface of the sleeve is arranged axially above an upper end surface of the housing. When the upper end surface of the housing is arranged axially above the upper end surface of the sleeve, the efficiency of the motor is degraded. However, when the upper end surface of the sleeve is arranged axially above the upper end surface of the housing, the upper end surface of the sleeve may come in contact with the lower surface of the rotor hub, and the upper end surface in which the dynamic pressure generating grooves are formed may be worn out. The scratches and the damages on the surface in which the dynamic pressure generating grooves are formed may cause the seizure of the bearing unit and the like troubles.